Date:	Wed, 23 Feb 2011 21:06:38 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Andres Salomon <dilinger@...ued.net>
Cc:	Daniel Drake <dsd@...top.org>, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org,
	"David S. Miller" <davem@...emloft.net>, sparclinux@...r.kernel.org
Subject: Re: [PATCH] of/pdt: allow DT device matching by fixing 'name'
 brokenness (v2)

On Wed, Feb 23, 2011 at 04:16:30PM -0800, Andres Salomon wrote:
> On Wed, 23 Feb 2011 16:28:15 -0700
> Grant Likely <grant.likely@...retlab.ca> wrote:
> 
> > On Wed, Feb 23, 2011 at 03:03:57PM -0800, Andres Salomon wrote:
> > > 
> > > Commit e2f2a93b changed dp->name from using the 'name' property to
> > > using package-to-path.  This fixed /proc/device-tree creation by
> > > eliminating conflicts between names (the 'name' property provides
> > > names like 'battery', whereas package-to-path provides names like
> > > '/foo/bar/battery@0', which we stripped to 'battery@0').  However,
> > > it also breaks of_device_id table matching.
> > > 
> > > The fix that we _really_ wanted was to keep dp->name based upon
> > > the name property ('battery'), but based dp->full_name upon
> > > package-to-path ('battery@0').  This patch does just that.
> > > 
> > > This also changes OLPC behavior to use the full result from
> > > package-to-path for full_name, rather than stripping the directory
> > > out.  In practice, the strings end up being exactly the same; this
> > > change saves time, code, and memory.
> > > 
> > > Note that this affects sparc by reverting dp->name back to what
> > > sparc was originally doing (looking at the name property).
> > > 
> > > v2: combine two patches and revert of_pdt_node_name to original
> > > version.
> > > 
> > > Signed-off-by: Andres Salomon <dilinger@...ued.net>
> > 
> > Hi Andres, comments below.
> > 
> > g.
> > 
> > > ---
> > >  drivers/of/pdt.c |   42 +++++++++++++++---------------------------
> > >  1 files changed, 15 insertions(+), 27 deletions(-)
> > > 
> > > diff --git a/drivers/of/pdt.c b/drivers/of/pdt.c
> > > index 28295d0..a7aa85e 100644
> > > --- a/drivers/of/pdt.c
> > > +++ b/drivers/of/pdt.c
> > > @@ -134,7 +134,7 @@ static char * __init
> > > of_pdt_get_one_property(phandle node, const char *name) 
> > >  static char * __init of_pdt_try_pkg2path(phandle node)
> > >  {
> > > -	char *res, *buf = NULL;
> > > +	char *buf = NULL;
> > >  	int len;
> > >  
> > >  	if (!of_pdt_prom_ops->pkg2path)
> > > @@ -147,29 +147,6 @@ static char * __init
> > > of_pdt_try_pkg2path(phandle node) pr_err("%s: package-to-path
> > > failed\n", __func__); return NULL;
> > >  	}
> > > -
> > > -	res = strrchr(buf, '/');
> > > -	if (!res) {
> > > -		pr_err("%s: couldn't find / in %s\n", __func__,
> > > buf);
> > > -		return NULL;
> > > -	}
> > > -	return res+1;
> > > -}
> > > -
> > > -/*
> > > - * When fetching the node's name, first try using package-to-path;
> > > if
> > > - * that fails (either because the arch hasn't supplied a PROM
> > > callback,
> > > - * or some other random failure), fall back to just looking at the
> > > node's
> > > - * 'name' property.
> > > - */
> > > -static char * __init of_pdt_build_name(phandle node)
> > > -{
> > > -	char *buf;
> > > -
> > > -	buf = of_pdt_try_pkg2path(node);
> > > -	if (!buf)
> > > -		buf = of_pdt_get_one_property(node, "name");
> > > -
> > >  	return buf;
> > >  }
> > >  
> > 
> > It seems to me that of_pdt_build_full_name will still be missing the
> > '@<addr>' component on non-sparc non-olpc builds because it uses the
> > broken of_pdt_node_name().  That needs to be fixed too, even if there
> > are no current users (or removed).
> 
> 
> The intent if for them to use the pkg2path hook.  If
> they can't use that, they'll need an architecture-specific way to
> figure out the @<addr> component.  It may even be possible for sparc
> to use package-to-path; but either way, if an architecture doesn't
> have package-to-path (OLPC and powerpc have it; I don't know about
> sparc), and can't fake it, it'll need to do something special.
> 
> If the pkg2path hook isn't set and we're not sparc, we fall back to
> dp->name.  That sucks, but I don't know of a better way to do things.

More that sucks, it is just plain *wrong*.  :-)

so, to sum up, of_pdt_build_tree goes through the following process:

1) dp = of_pdt_create_node
  - dp->name = of_pdt_get_one_property(node, "name"); /* name w/o addr */

2) (SPARC) dp->path_component_name = build_path_component(dp);
  - format <node name>@<address>
  - uses dp->name value
  - not on OLPC

3) dp->full_name = of_pdt_build_full_name(dp)
  - (SPARC) use dp->path_component_name
  - (OLPC) depend on value from of_pdt_try_pkg2path(node);
  - (others) fake it with an incorrect value?

Am I correct?

Faking it is clearly not acceptable.  The solution is to *force* all
platforms to implement a method for obtaining the full path.  That
means BUG() or WARN() if pkg2path is not populated, or if it returns
NULL.  It also means no mucking about with of_pdt_try_pkg2path().
Call ops->pkg2path directly and complain loudly when it does not work.

I see two choices:
1) implement ops->pkg2path for SPARC, but back it with
   build_path_component() instead of a call to OF
2) #ifdef of_pdt_build_full_name() to use the current behaviour for
   SPARC, but call pkg2path for everyone else.

Actually, I'd like to see build_path_component() refactored to return
the full_name instead.  It is trivial to get the path component from
the full name at any time, but it is not trivial to go the other
direction.... but that is probably more surgery than should be done in
this immediate bug-fix.  I'm assuming a fix is necessary before 2.6.38
is finalized?

g.
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